Since Isaac made landfall more than a week ago, the water from the storm has receded and tar balls and oil have been reported on shores in Alabama and Louisiana, where officials closed a 13-mile stretch of beach Tuesday.

BP said Wednesday some of that oil was from the spill, but said some of the crude may be from other sources, too.

"If there's something good about this storm, it made it visible, where we can clean it up," BP spokesman Ray Melick said.

BP still has hundreds of cleanup workers on the Gulf Coast after the Deepwater Horizon drilling rig exploded, killing 11 workers and leading to the nation's largest offshore spill.

Melick said the company was working with the Coast Guard, state officials and land managers to clean up the oil on the Fourchon beach in Louisiana. He said crews would be there Thursday.

Isaac made landfall near Fourchon on Aug. 28 as a Category 1 storm, pummeling the coast with waves, wind and rain. Seven people were killed in Louisiana and Mississippi.

Ed Overton, a chemist and oil spill expert at Louisiana State University, said the exposed oil was weathered and less toxic, though it could still harm animals - such as crabs, crawfish and bait fish.

He said the storm helped speed up natural processes that break down oil and it might take several more storms to stir up the rest of the oil buried along the coast.

"We don't like to say it, but hurricanes are Mother Nature's way of taking a bath," he said.

The reappearance of oil frustrated state officials.

Garret Graves, a top coastal aide to Louisiana Gov. Bobby Jindal, accused BP of not being aggressive enough with its initial cleanup.

"If they would put just a fraction of the dollars they're putting into their PR campaign into cleanup, we'd certainly be much farther ahead than we are now," he said.

BP has spent millions of dollars on its public relations campaign, but the company has not said exactly how much it has invested. Its cleanup and response costs over the last two years were more than $14 billion and more than 66 million man-hours have gone to protect and treat the Gulf shoreline, the company has said.

BP also gave $1 million to the American Red Cross and The Salvation Army to help victims of Isaac.

Along the oiled Fourchon beach, officials restricted fishing in waters extending one mile offshore. The state Wildlife and Fisheries Department said there was a large mat of tar on one beach and concentrations of tar balls on nearby shores.

In Alabama, officials said the tar was more of an unsightly nuisance than a health hazard, describing globs as ranging in size from a dime to a half dollar coin.

"There are areas where there are significant deposits," said Phillip West, coastal resources manager in Orange Beach, Ala.

Samples from both states were being tested to determine whether the tar was from BP's Macondo well.

The Alabama cities believe the tar hitting their white-sand beaches was breaking off large, submerged mats from the spill.

"I do believe we are going to be dealing with this for years," said Grant Brown, a spokesman for the city of Gulf Shores, Ala.

The areas where workers found tar after the storm were some of the same places the heaviest oil deposits occurred during the spill.

In Mississippi, officials have so far spotted only about a couple dozen tar balls on beaches. Most have turned out to be reddish-brown bacteria, which commonly washes ashore after storms.